Update to build against newer versions of Rust

This code currently only seems to build with rust 1.56, but rust has moved on quite a bit from there and a number of our dependencies have now advanced past the point where they will even be able to be built with rust 1.56.

Unfortunately, trying to build our code against newer rust throws up a bunch of errors, so presumably we have been doing something bad that we should stop doing.

Start by attempting to build the project with a Rust version newer than 1.56 and record the compiler errors, then inspect the dependency configuration and the code paths identified by those errors. Done means the project builds successfully with a newer Rust toolchain and dependencies that no longer support Rust 1.56.

Written by the indexing model from the issue text.